For an AC microgrid, frequency regulation is an important functional block in the \(\mu \) MS design, expecially when the microgrid enters the islanded or hybrid mode. Similar to bulk transmission systems, frequencies at the microgrid can be regulated in a hierarchical manner. The bottom layer of the frequency regulation entails local controller in DERs, e.g., power controllers of inverter-based resources (IBRs), and governors of small synchronous generators. These local controllers are termed the primary control of microgrids [1]}, [2]}. As the primary control can yield steady-state errors of frequencies from their nominal values after a disturbance, a secondary control layer is needed in microgrids to regain the nominal frequency [3]}, [4]}. Since the secondary frequency regulation in AC microgrids shares a very similar objective with the Automatic Generation Control (AGC) of bulk transmission systems, we term the secondary frequency regulator in microgrids Micro-AGC (\(\mu \) AGC) to highlight its connection with the AGC that has served the bulk power systems for half of a century. This paper focuses on the \(\mu \) AGC design.
